• Thomas R Salas, Shrikanth A Reddy, John L Clifford, Roger J Davis, Akira Kikuchi, Scott M Lippman, and David G Menter.
• Departments of Clinical Cancer Prevention and Gastrointestinal Medical Oncology, The University of Texas M D Anderson Cancer Center, Houston, Texas 77030, USA.
• J. Biol. Chem. 2003 Oct 17; 278 (42): 41338-46.

AbstractGlycogen synthase kinase-3beta (GSK-3beta) activity is suppressed when it becomes phosphorylated on serine 9 by protein kinase B (Akt). To determine how GSK-3beta activity opposes Akt function we used various methods to alleviate GSK-3beta suppression in prostate carcinoma cells. In some experiments, LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (a kinase involved in activating Akt) and tumor necrosis factor-alpha (TNF-alpha) were used to activate GSK-3beta. In other experiments mutant forms of GSK-3beta, GSK-3betadelta9 (a constitutively active deletion mutant of GSK-3beta) and GSK-3betaY216F (an inactive point mutant of GSK-3beta) were used to alter GSK-3beta activity. LY294002, TNF-alpha, and overexpression of wild-type GSK-3beta or of GSK-3betadelta9, but not GSK-3betaY216F, alleviated the suppression of GSK-3beta activity in prostate carcinoma cells and enhanced the turnover of beta-catenin. Forced expression of wild-type GSK-3beta or of GSK-3betadelta9, but not GSK-3betaY216F, suppressed cell growth and showed that the phosphorylation status of GSK-3beta can affect its intracellular distribution. When transcription factors activator protein-1 and cyclic AMP-response element (CRE)-binding protein were analyzed as targets of GSK-3beta activity, overexpression of wild-type GSK-3beta suppressed AP1-mediated transcription and activated CRE-mediated transcription. Overexpression of GSK-3betadelta9 caused an (80-fold) increase in CRE-mediated transcription, which was further amplified (up to 130-fold) by combining GSK-3betadelta9 overexpression with the suppression of Jun activity. This study also demonstrated for the first time that expression of constitutively active GSK-3betadelta9 results in the phosphorylation of CRE-binding protein on serine 129 and enhancement of CRE-mediated transcription in intact cell nuclei.

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